The instant invention is directed in general to optical systems in which a laser beam is injected into the end of an optical fiber and, more specifically, to laser based material processing systems in which a high power laser beam is injected into the fiber input end for transmission to a remote end of the fiber where materials processing is performed with the emitted beam.
Laser based materials processing as known in the art and as used herein, refers to performance of processes such as cutting, welding, drilling and soldering, using a continuous wave or pulsed laser beam. The average power of such a laser beam may range from as little as approximately one watt to thousands of watts, the specific power being selected on the basis of the particular processing being performed. It is known in the art to transmit the laser beam from the laser to the vicinity of the workpiece by means of an optical fiber. Apparatus and methods for injecting a laser beam into an optical fiber for transmission there through are disclosed in commonly assigned U.S. Pat. Nos. 4,564,736; 4,676,586; and 4,681,396 respectively entitled "Industrial Hand Held Laser Tool and Laser System", "Apparatus and Method for Performing Laser Material Processing Through a Fiber Optic", and "High Power Laser Energy Delivery System", the disclosures of these patents being incorporated in their entirety herein by reference.
A problem associated with high power optical fiber injection techniques is that high power lasers tend to ionize the air at the focal point of the focusing lens used to inject the laser into the optical fiber end. This occurs due to the extremely high energy densities present. Ionization of this type causes several problems with injection techniques.
First, ionization of the air in front of the optical fiber causes damage during injection because it causes debris to deposit on the optical fiber face. This debris in the air (usually dust) is a catalyst for breakdown because the debris is absorbing at many laser wavelengths. When the debris in the air is deposited on the optical fiber face, due to the ionization, the debris makes the fiber face absorbing to the wavelength being used, causing fiber damage.
Second, ionization of the air generates a hot plasma. When the air closest to the fiber injection face is ionized and the ionization generates this hot plasma, the fiber tip will melt. This condition results in burning of the fiber injection end and failure in the injection process.
Upon the occurrence of each need to replace a damaged optical fiber, the time required to effect fiber injection represents manufacturing downtime and therefore manufacturing cost and inefficiency. Furthermore, additional costs may be necessary in order to repair or replace any damaged optical fibers. Therefore, fiber injection must be completed without the high power beam damaging the optical fiber.
Therefore, it is apparent from the above that there exists a need in the art for an apparatus and method for high power laser fiber beam injection which prevents ionization of the air surrounding the optical fiber injection face or around the optical fiber entirely. It is a purpose of this invention, to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.